Disk devices such as a magnetic disk device include, for example, a magnetic disk provided inside a case, spindle motor which supports and rotates the magnetic disk, magnetic head which reads/writes data from/to the magnetic disk, and carriage assembly which supports the magnetic head movably with respect to the magnetic disk. The magnetic head includes a head part composed of a magnetic recording head used for write and a resuming head used for read.
In recent years, perpendicular magnetic recording heads are proposed for increasing recording density, capacity, and miniaturization of the magnetic disk device. In such magnetic heads, a recording head includes a main magnetic pole which produces a perpendicular magnetic field, write shield disposed to face the main magnetic pole with a write gap interposed therebetween at a trailing side of the main magnetic pole to close a magnetic path with the magnetic disk, and coil to supply a magnetic flux to the main magnetic pole.
There are proposed microwave-assisted magnetic recording heads in which a spin torque oscillator arranged between the main magnetic pole and the write shield (arranged in the write gap). The spin torque oscillator (STO) is formed as a layered structure of a field generation layer (FGL), intermediate layer, and spin injection layer face (SIL), and the spin torque oscillator is electrically connected to the main magnetic pole and the write shield. The intermediate layer functions to send spin current from the spin injection layer (SIL) to the field generation layer (FGL); however, the conventional layered structure does not sufficiently inject the polarized spin into the field generation layer (FGL), and when bias current increases, the magnetization of the spin injection layer (SIL) tends to fluctuate by the spin transfer torque from the field generation layer (FGL).